Blank epub on Kobo?

I just purchased "My Little Sister Can Read Kanji" and downloaded the Premium Epub using a token. The problem is, when I transferred it to my Kobo Aura eReader I only got a blank screen. The cover preview is black and if I open it I get a single white page. This is the 3rd ebook I purchased from you guys (with Grimgar and My Big Sister Lives in a Fantasy World) and both of those did not have this issue. If I try opening the epub using a desktop app, I can read it just fine.

I have tried re-downloading the file, I factory reset my eReader and I am running out of ideas.

@Gilyu I will look into this asap. We don't get many sales on Kobo, you might be the first person to notice.

I'll try testing this on my own Kobo shortly... I used an identical template as before, but it's possible that I introduced some incompatibility somehow. Perhaps it has something to do with the usage of kanji characters occasionally in the text? Perhaps try changing the font. Even so that shouldn't cause the entire book not to display.

I don't know the cause and am trying to figure out what if anything changed from the format of the other two books... It passes epub3 verification so it's still a bit of a mystery, and kobo doesn't provide a simulator or debug logs as far as I know.
Working on it.

Edit: Found multiple stack trace files hidden on my kobo: Looks like the epub is actually crashing the device.

Okay, so I was fully prepared to come in here apologizing for some kind of boneheaded typo that was screwing up something that I didn't catch.
But no, I am not apologizing at all for this. This is 100% kobo (and the underlying Adobe Digital Reader library) being shitty.

So I literally went through line by line removing content from the ebook, trying to see what was causing it to crash. I ended up removing everything but the cover, and it STILL crashed!

So I thought, maybe it was the CSS stylesheet? Well, but that was identical to Grimgar's stylesheet... EXCEPT for 1 extra style I added for a certain scene in SisKan which needed the 1 sentence to be vertically centered on the page, so I used some CSS 3:
.vertical-center {
margin: 50vh 0 0 0l;
}

This style caused Kobo to crash completely. Oddly enough, I also use the "vh" measures for the image displays, but those don't crash. Only when I tried to use it in a margin command, I guess.

So mystery solved! By the time you read this the version you download from out website should be updated, so please redownload and enjoy!

@Pmf96 to be honest I came into this fully realizing that ereaders are a mess of incompatibilities and bugs.

I figured from the start there would be a bit of a learning curve as we figured out exactly what worked on what devices and how.
I didn't expect some perfectly valid CSS 3 to actually crash a device though.

@Sam-Pinansky Hmmm... I don't have any knowledge about that. But I do appreciate a lot the manner and how fast the problem got fixed. Plus, even though that you didn't have to do it, you kept updating us while you were making progresses and that's really nice :smile: